The present invention relates to a lighting device and an image display device including the same as a backlight.
Besides being used for general illumination purposes, for example, for indoor and outdoor lighting, lighting devices are also used as backlight devices for non-luminescent display devices such as liquid crystal display devices. Lighting devices for use as backlight devices, in particular, are required to be low power consuming and durable, so that they use, in many cases, LEDs (light emitting diodes) as light sources.
Lighting devices using LEDs as light sources, particularly, planar lighting devices each have a wide light emitting surface for illuminating a wide area. Such planar lighting devices each have an optical system for forming light emitted from the LEDs into a uniform planar light source. Known techniques for realizing such planar lighting devices include one disclosed in Japanese Unexamined Patent Application Publication No. 2006-236701. The backlight device described in the above patent document has a light guide plate including a groove-like concave portion on which side lighting LEDs are disposed and a diffuse reflection member provided on the underside of the light guide plate. The diffuse reflection member serves to uniformize brightness distribution so as to cause the liquid crystal panel of the planar lighting device to be uniformly irradiated with light.